Liquid crystal display device

Abstract

To provide a display device having a high reflectance and achieving high-quality white display and black display without coloring and excellent color display.SOLUTION: The display device includes a substrate (A) having the following polarization functions. When two of the substrates disposed with the absorption axes parallel to each other are measured to obtain a transmittance, the average transmittance from 520 nm to 590 nm is 30% or more, the difference in an absolute value between the average transmittance from 420 nm to 480 nm and the average transmittance from 520 nm to 590 nm is within 5%, and the difference in an absolute value between the average transmittance from 520 nm to 590 nm and the average transmittance from 590 nm to 660 nm is within 5%. When the two of the substrates disposed with the absorption axes orthogonal to each other are measured to obtain a transmittance at each wavelength, the difference in an absolute value between the average transmittance from 420 nm to 480 nm and the average transmittance from 520 nm to 590 nm is within 2%, and the difference in an absolute value between the average transmittance from 520 nm to 590 nm and the average transmittance from 600 nm to 660 nm is within 2%.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a liquid crystal display device.

Background Art

[0002] A polarizing element is generally manufactured by adsorbing and aligning iodine, which is a dichroic dye, or a dichroic dye on a polyvinyl alcohol resin film. A protective film made of triacetyl cellulose or the like is bonded to at least one side of this polarizing element via an adhesive layer to form a polarizing plate, which is used in a liquid crystal display device or the like. A polarizing plate using iodine as a dichroic dye is called an iodine-based polarizing plate, while a polarizing plate using a dichroic dye as a dichroic dye is called a dye-based polarizing plate. Among these, the dye-based polarizing plate has characteristics such as high heat resistance, high humidity and heat durability, and high stability, and also has high color selectivity by blending. However, it has a problem that its transmittance is lower than that of an iodine-based polarizing plate having the same contrast. Therefore, it has been difficult to maintain high durability, have diverse color selectivity, and achieve a higher transmittance.

[0003] However, even in such a dye-based polarizing plate with diverse color selectivity, the conventional polarizing elements are polarizing elements that exhibit a yellowish color when the absorption axes are installed in parallel. On the other hand, the color of one iodine-based polarizing plate is a polarizing element that exhibits yellow-green when the absorption axes are installed in parallel and blue when the absorption axes are installed orthogonally. When using such a polarizing plate in a display device (hereinafter, also referred to as a display), the color of the polarizing element greatly affects the display characteristics. In particular, in a display device using liquid crystals, it is essential to provide at least one polarizing element on the observer side via a liquid crystal cell. Therefore, it is clear that the color of the polarizing plate can be confirmed by the observer. However, the color development due to the wavelength characteristics of such a polarizing element is one of the elements that greatly affect the display characteristics of the display. In a conventional transmissive liquid crystal device using a backlight, it is necessary to optimize the display color by adjusting the spectral distribution of the backlight and the color filter.

[0004] On the other hand, in a display device that uses ambient light, particularly a reflective liquid crystal device, since the spectrum of the light source cannot be adjusted like a transmissive display, the wavelength characteristics of the polarizing plate directly become the display color. For this reason, improving the wavelength characteristics of the polarizing plate has been an important issue. Conventional reflective liquid crystal devices have a slightly yellowish white display and a bluish black display. Therefore, compared with other reflective devices (such as electronic paper displays), the display quality has been regarded as inferior.

[0005] In addition, as a polarizing plate for improving the display performance of a display, a polarizing plate using a method of adjusting the spectrum of a color filter or mixing a dye into an adhesive or the like to adjust the display color has been proposed. However, all of them result in a decrease in the transmittance of the polarizing plate and also cost, so great improvement is required. Also, although the wavelength characteristics of the polarizing plate have been improved, in a generally used iodine-based polarizing plate, when the transmittance spectrum (when the absorption axis is parallel) is made uniform at each wavelength, light leakage occurs at short wavelengths when orthogonal, and sufficient display could not be achieved. As a method for improving the hue of this polarizing plate, techniques such as those in Patent Document 1 or Patent Document 2 are disclosed.

[0006] Patent Document 1 discloses a polarizing plate that calculates a neutrality coefficient and has an absolute value of 0 to 3. Patent Document 2 discloses a polarizing element that, at a transmittance of 410 nm to 750 nm, is within ±30% of the average value and is adjusted by adding a direct dye, a reactive dye, or an acid dye in addition to iodine. The polarizing element disclosed in the same document is a polarizing element obtained by making the absolute value within 2 of the a value and b value in the UCS color space of the color when measured using only one polarizing element, that is, the single transmittance.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

[0008] [Non-Patent Document 1] Application of Functional Dyes, 1st Edition, CMC Publishing Co., Ltd., Supervised by Masahiro Irie, P98-100 [Non-Patent Document 2] Dye Chemistry, by Yutaka Hosoda, Gihodo [Non-Patent Document 3] A book on understanding liquid crystals, published by Kogyo Chosakai Publishing, by Shohei Naemura, Q58-Q59 [Non-Patent Document 4] A book that explains the mechanism of liquid crystals with illustrations and diagrams, Gijutsuhyoronsha, Hideo Takezoe, Yoichi Takanishi, Koichi Miyaji, p.182 Summary of the Invention [Problem to be solved by the invention]

[0009] However, as can be seen from the examples in Patent Document 1, even if the neutral coefficient (Np) is low, the color is yellowish green when expressing white, since the a* value is -2 to -1 and the b* value is 2.5 to 4.0 even for the parallel hue calculated by JIS Z 8729. Moreover, although the a* value for the orthogonal hue is 0 to 1, the b* value is -1.5 to -4.0, resulting in a polarizing plate that exhibits a blue color.

[0010] In addition, in Patent Document 2, the polarizing element is a polarizing element obtained by setting the single transmittance, that is, the color measured using only one polarizing element, to within an absolute value of 2 in terms of the a and b values ​​in the UCS color space. However, it is not possible to simultaneously express achromatic colors in the hues of white display (when parallel) and black display (when perpendicular) using two polarizing plates. In addition, as can be seen from the examples, the average single transmittance is 31.95% in Example 1 and 31.41% in Example 2, and since the transmittance is low, it does not have sufficient performance in fields requiring high transmittance, particularly in fields such as liquid crystal display devices and organic electroluminescence.

[0011] Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide a display device that can achieve high-quality white display, black display, and excellent color display without coloring while having a high reflectance.

Means for Solving the Problems

[0012] As a result of intensive studies to solve the above problems, the present inventors have found that a substrate having a polarization function containing an azo compound, in which the average transmittance at each wavelength obtained by measuring with the absorption axes of two substrates parallel is 30% or more in the wavelength range of 520 nm to 590 nm, the absolute value of the difference between the average transmittance in the wavelength range of 420 nm to 480 nm and the average transmittance in the wavelength range of 520 nm to 590 nm is within 5%, and the absolute value of the difference between the average transmittance in the wavelength range of 520 nm to 590 nm and the average transmittance in the wavelength range of 590 nm to 660 nm is within 5%. Further, in the transmittance at each wavelength obtained by measuring with the absorption axes of two substrates orthogonal to each other, the absolute value of the difference between the average transmittance in the wavelength range of 420 nm to 480 nm and the average transmittance in the wavelength range of 520 nm to 590 nm is within 2%, and the absolute value of the difference between the average transmittance in the wavelength range of 520 nm to 590 nm and the average transmittance in the wavelength range of 600 nm to 660 nm is within 2%. A display device provided with a substrate (A) can express high-quality white and black without coloring while having a high reflectance, and can provide a display device capable of sufficient color display as a reflective type. Based on this finding, the present invention has been completed.

[0013] That is, the present invention is (1) containing an azo compound or a salt thereof, in the transmittance obtained by measuring with the absorption axes of two substrates parallel, the average transmittance in the wavelength range of 520 nm to 590 nm is 30% or more, the absolute value of the difference between the average transmittance in the wavelength range of 420 nm to 480 nm and the average transmittance in the wavelength range of 520 nm to 590 nm is within 5%, and the absolute value of the difference between the average transmittance in the wavelength range of 520 nm to 590 nm and the average transmittance in the wavelength range of 590 nm to 660 nm is within 5%, and Furthermore, in each wavelength transmittance obtained by measuring the absorption axes of two base materials orthogonally, the absolute value of the difference between the average transmittance of 420 nm to 480 nm and the average transmittance of 520 nm to 590 nm is within 2%, and the absolute value of the difference between the average transmittance of 520 nm to 590 nm and the average transmittance of 600 nm to 660 nm is within 2%. A display device characterized by comprising a base material (A) having a polarization function.

[0014] (2) The display device according to (1), characterized by comprising a color filter.

[0015] (3) The NTSC ratio when light passes through the color filter twice is from 1 to 20. The display device according to (2).

[0016] (4) The color filter includes a red color layer, a green color layer, and a blue color layer. The display device according to (2) or (3).

[0017] (5) The color filter includes a red color layer, a green color layer closer to red, a blue color layer, and a green color layer closer to blue. The display device according to (2) or (3).

[0018] (6) The color filter has a colorless and transparent region. The display device according to (2) to (5).

[0019] (7) The area of the colorless and transparent region is 1 / 4 or more of the total area of the color filter. The display device according to (6).

[0020] (8) Furthermore, in each wavelength transmittance obtained by measuring the absorption axes of two base materials (A) orthogonally, the absolute value of the difference between the average transmittance of 420 nm to 480 nm and the average transmittance of 520 nm to 590 nm is greater than 0.3%, and The display device according to any one of (1) to (7), characterized in that the absolute value of the difference between the average transmittance of 520 nm to 590 nm and the average transmittance of 600 nm to 660 nm is greater than 0.3%.

[0021] (9) The display device according to any one of (1) to (8), characterized in that the display device is a liquid crystal display device.

[0022] (10) The display device according to (9), characterized in that the liquid crystal display device is a reflective liquid crystal display device.

[0023] (11) The display device according to any one of (2) to (10), characterized in that at least a reflector, a substrate (A), a liquid crystal layer, a color filter, and a substrate (A) are arranged in this order from the back side of the display device.

[0024] (12) The display device according to (11), characterized in that the liquid crystal layer is arranged in this order from the back side as a reflective electrode, a liquid crystal layer, and a transparent electrode.

[0025] (13) The display device according to (11) or (12), characterized in that the reflector is a diffusive reflector.

[0026] (14) The display device according to (12), characterized in that the reflective electrode is a diffusive reflector.

[0027] (15) The display device according to any one of (11) to (14), characterized in that a substrate having a light diffusion function is provided between the substrate (A) and the liquid crystal layer.

[0028] (16) The display device according to any one of (1) to (15), characterized in that a substrate having a retardation value of 120 to 160 nm and the substrate (A) are laminated.

Advantages of the Invention

[0029] The display device of the present invention can achieve high-quality white display, black display, and excellent color display without coloring while having a high reflectance.

Brief Description of the Drawings

[0030]

Figure 1

Figure 2

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Figure 4

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Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0031] In the present invention, a base material having a polarizing function containing an azo compound, in each wavelength transmittance obtained by measuring with the absorption axes of the two base materials parallel, the average transmittance at 520 nm to 590 nm is 30% or more, the absolute value of the difference between the average transmittance at 420 nm to 480 nm and the average transmittance at 520 nm to 590 nm is within 5%, and the absolute value of the difference between the average transmittance at 520 nm to 590 nm and the average transmittance at 590 nm to 660 nm is within 5%, and Furthermore, in each wavelength transmittance obtained by measuring with the absorption axes of the two base materials orthogonal to each other, the absolute value of the difference between the average transmittance of 420 nm to 480 nm and the average transmittance of 520 nm to 590 nm is within 2%, and The present invention relates to a display device characterized by comprising a base material (A) characterized in that the absolute value of the difference between the average transmittance of 520 nm to 590 nm and the average transmittance of 600 nm to 660 nm is within 2%.

[0032] (Regarding the base material (A)) Regarding the transmittance of the display device provided with the base material (A) of the present invention, the average transmittance of each wavelength of 520 nm to 590 nm obtained by measuring with the absorption axes of two base materials (A) parallel is 30% or more. Thereby, the display device provided with the base material (A) of the present invention can be bright and have a high luminance.

[0033] In particular, each wavelength of 520 nm to 590 nm is the wavelength with the highest visual sensitivity based on the isochromatic function used in the calculation when indicating color in JIS Z 8701. Since the transmittance of each wavelength in this range is close to the transmittance that can be visually confirmed, it is important to control the transmittance of each wavelength of 520 nm to 590 nm to 30% or more.

[0034] For example, the average transmittance of 520 nm to 590 nm obtained by measuring with the absorption axes of two base materials parallel and the visually corrected parallel transmittance obtained with the absorption axes of two base materials parallel show almost the same value. From this, it can be understood that it is very important to adjust the transmittance of 520 nm to 590 nm.

[0035] The required transmittance of the display device is 30% to 45% as the average transmittance of each wavelength of 520 nm to 590 nm obtained by measuring with the absorption axes of two base materials (A) parallel, preferably 35% to 40%, and more preferably 36% to 37%. The degree of polarization at that time may be 50% to 100%, preferably 60% to 100%, and more preferably 70% to 100%.

[0036] Although a higher degree of polarization is preferable, increasing the degree of polarization tends to reduce the transmittance. Therefore, it is necessary to select a polarizing element with a degree of polarization suitable for the display device in relation to the relationship between the degree of polarization and the transmittance.

[0037] In the present invention, in the transmittance at each wavelength obtained by measuring with the absorption axes of two substrates (A) parallel, not only the average transmittance of 520 nm to 590 nm, but also the average transmittance of 420 nm to 480 nm and the average transmittance of 520 nm to 590 nm It is also necessary that the absolute value of the difference from the average transmittance of 590 nm to 660 nm is within 5%. Each wavelength of 420 nm to 480 nm, 520 nm to 590 nm, and 590 nm to 660 nm is a main wavelength band based on the equal-color function used in the calculation when indicating color in JIS Z 8729.

[0038] Specifically, in the XYZ equal-color function of JIS Z 8701, which is the basis of JIS Z 8729, when the maximum values of x(λ) with a maximum value of 600 nm, y(λ) with a maximum value of 550 nm, and z(λ) with a maximum value of 455 nm are set to 100, the wavelengths showing values of 20 or more are each wavelength of 420 nm to 480 nm, 520 nm to 590 nm, and 590 nm to 660 nm.

[0039] Using a polarizing element or polarizing plate in which the transmittances at those wavelengths of 420 nm to 480 nm, 520 nm to 590 nm, and 590 nm to 660 nm are adjusted to a predetermined transmittance as the substrate (A) having a polarizing function, and by using the substrate (A), the display device of the present application can be achieved. The adjustment range is such that, in the transmittance at each wavelength obtained by measuring with the absorption axes of two substrates (A) parallel, the absolute value of the difference between the average transmittance of 420 nm to 480 nm and the average transmittance of 520 nm to 590 nm is required to be within 5%, preferably within 3%.

[0040] In addition, it is also necessary to adjust the predetermined transmittance for each wavelength transmittance obtained by measuring the absorption axes of two sheets of the base material (A) orthogonally. The absolute value of the difference between the average transmittance in the range of 420 nm to 480 nm and the average transmittance in the range of 520 nm to 590 nm is within 2%, and it is necessary that the absolute value of the difference between the average transmittance in the range of 520 nm to 590 nm and the average transmittance in the range of 600 nm to 660 nm is within 2%.

[0041] Furthermore, for each wavelength transmittance obtained by measuring the absorption axes of two sheets of the base material (A) orthogonally, the absolute value of the difference between the average transmittance in the range of 420 nm to 480 nm and the average transmittance in the range of 520 nm to 590 nm needs to be within 2%, preferably within 1%. Also, the absolute value of the difference between the average transmittance in the range of 520 nm to 590 nm and the average transmittance in the range of 590 nm to 660 nm needs to be within 2%, preferably within 1%.

[0042] Moreover, for each wavelength transmittance obtained by measuring the absorption axes of two sheets of the base material (A) orthogonally, the absolute value of the difference between the average transmittance in the range of 420 nm to 480 nm and the average transmittance in the range of 520 nm to 590 nm needs to be greater than 0.3% due to process issues, preferably 0.5% or more. Also, the absolute value of the difference between the average transmittance in the range of 520 nm to 590 nm and the average transmittance in the range of 590 nm to 660 nm needs to be greater than 0.3% due to process issues, preferably 0.5% or more. Here, the process issues refer to the unevenness in dyeing when multiple azo dyes are mixed for dyeing.

[0043] On the other hand, although adjustment of the average transmittance in the ranges of 380 nm to 420 nm, 480 nm to 520 nm, and 660 nm to 780 nm is also necessary, since the ranges of 420 nm to 480 nm, 520 nm to 590 nm, and 600 nm to 660 nm are adjusted, they are not likely to be greatly affected by the pigment, so adjustment may not be necessary.

[0044] In a reflective liquid crystal display device, it is important to increase the reflectivity. This is because it is necessary to ensure sufficient visibility even in a relatively dark environment such as indoors. However, in a color reflective liquid crystal display device, the reflectivity has been reduced because the transmittance of the color filter is low. As a diagram showing that the reflectivity is reduced by the color filter, Fig. 1 shows a diagram representing the relationship between the NTSC ratio and the transmittance when light passes through the color filter twice.

[0045] Here, the NTSC ratio when light passes through the color filter twice is the area obtained by plotting the chromaticities when light passes through each color element of the color filter twice on the chromaticity (x, y) diagram of the CIE1931 XYZ color system and connecting them with a straight line, and the ratio to the area of the triangle formed by the three primary colors, red (0.670, 0.330), green (0.210, 0.710), and blue (0.140, 0.080), which are defined by the standard method in the chromaticity (x, y) of the CIE1931 XYZ color system by the National Television Standards Committee, expressed as a percentage.

[0046] Also, in a color reflective liquid crystal display device, since external light passes through the color filter twice, the NTSC ratio of the color filter is taken as the NTSC ratio when light passes through twice.

[0047] From Fig. 1, it can be seen that when the NTSC ratio is large, the transmittance is low, but as the NTSC ratio decreases, the transmittance increases. Therefore, to increase the reflectivity of a color reflective liquid crystal display device, it is only necessary to increase the transmittance, that is, to decrease the NTSC ratio. In our research on color reflective liquid crystal display devices, we have found that in a color reflective liquid crystal display device, even when the NTSC ratio is small, the human eye can sufficiently perceive colors. As a result, the value of the NTSC ratio at which the human eye can sufficiently perceive colors is 1% - 20%, preferably 1% - 10%, and more preferably 1% - 5%.

[0048] In a color reflective liquid crystal display device using a color filter with a small NTSC ratio, the reflectance is improved and the sensitivity of the human eye to colors is enhanced. Therefore, when using a conventional polarizing plate, coloring occurs in white display and / or black display, and visual recognition of this reduces the display quality. In a color reflective liquid crystal display device, it has been found that by simultaneously using a color filter with a small NTSC ratio and a substrate (A), for the first time, a bright color display with high reflectance and an excellent color display without coloring in white display and / or black display can be realized.

[0049] As a method of making the NTSC ratio of the color filter 1% - 20%, there are methods such as reducing the concentration of the dye or pigment forming the color layer, reducing the thickness of the color layer, and forming a transparent region without a color layer. In particular, in the method of forming a transparent region without a color layer, since coloring by the polarizing plate in the transparent region without a color layer can be suppressed, the use of the substrate (A) is particularly effective.

[0050] In the method of forming a transparent region without a color layer, it is necessary that the area of the transparent region without a color layer is 1 / 4 or more of the area of the entire region. Preferably, the area of the transparent region without a color layer is 1 / 2 or more of the area of the entire region. More preferably, the area of the transparent region without a color layer is 2 / 3 or more of the area of the entire region. Thereby, a color reflective liquid crystal with a bright color display having high transmittance, that is, high reflectance, can be realized.

[0051] By providing a polarizing element or a polarizing plate provided with the substrate (A) in the display device, the color expression of the display device can be controlled. In particular, when a polarizing element or a polarizing plate provided with the substrate (A) is provided in the display device in the same general usage, the hue based on the polarizing plate can be controlled, and the display device can express white like high-quality paper when displaying white, and can express jet-black when displaying black.

[0052] In a general polarizing plate, when controlled to express black, the white purity decreases in the transmittance when the polarizing elements are parallel, and it exhibits a yellow or yellow - green color. Conversely, when controlling the transmittance when the polarizing elements are parallel so as to be able to express white, the black purity decreases in the transmittance when the polarizing elements are orthogonal, and it exhibits a blue color. When a polarizing element having such a hue is provided in a display device, it is natural that the display device exhibits the hue of the polarizing element.

[0053] For such color rendering of this display device, in a conventional transmissive liquid crystal device using a backlight, the display color can be optimized by adjusting the spectral distribution of the backlight and the color filter. However, it was necessary to adjust the color of the polarizing plate by the backlight or the color filter.

[0054] However, in a reflective display device that uses external light for display, particularly in a reflective liquid crystal device, since there is no backlight, it is impossible to simultaneously improve the yellow color rendering during white display and the blue color rendering during black display with a color filter. Furthermore, in a display device that uses a polarizing plate for antireflection when it is desired to prevent reflection of external light, for example, when used in an organic electroluminescence display device (hereinafter abbreviated as OLED) or a plasma display, etc., the polarizing plate is provided together with a retardation plate on the side where a person observes, rather than on the side of the light - emitting display device.

[0055] In conventional general polarizing plates, since it reduces the color purity of the color emission of OLEDs, improving the hue of the polarizing plate has been very important. The formulation of the present invention is also effective for display devices such as OLEDs that want to control such reflected light. That is, in the present invention, it improves the color emission generated by the problems of yellow color rendering during white display and blue color rendering during black display that conventional polarizing plates have, and provides a display device that can display a high - quality white like that of high - grade paper during white display and a jet - black color during black display. In particular, in a reflective display, it has achieved the ability to improve the luminance during display and also improve the contrast.

[0056] (Method for producing polarizing element and polarizing plate of base material (A) of the present invention) As an element that may contain an azo compound, particularly generally a dichroic dye, for example, a film formed of a hydrophilic polymer is used. The hydrophilic polymer is not particularly limited, and examples thereof include polyvinyl alcohol-based resins, amylose-based resins, starch-based resins, cellulose-based resins, polyacrylate-based resins, and the like. When a dichroic dye is contained, a resin composed of a polyvinyl alcohol-based resin and its derivatives is most preferable in terms of processability, dyeability, crosslinkability, and the like. By forming these resins into a film shape, containing the dye of the present invention and its formulation, and applying an orientation treatment such as stretching, a polarizing element or a polarizing plate can be produced.

[0057] As the dichroic dye composed of an azo compound, for example, an organic compound as shown in Non-Patent Document 1 can be used. Particularly, those with high dichroism are preferable. For example, C.I. Direct Yellow 12, C.I. Direct Yellow 28, C.I. Direct Yellow 44, C.I. Direct Orange 26, C.I. Direct Orange 39, C.I. Direct Orange 107, C.I. Direct Red 2, C.I. Direct Red 31, C.I. Direct Red 79, C.I. Direct Red 81, C.I. Direct Red 247, C.I. Direct Green 80, C.I. Direct Green 59, and organic dyes described in JP-A-2001-33627, JP-A-2002-296417, and JP-A-60-156759 are exemplified.

[0058] These organic dyes can be used not only as free acids but also as alkali metal salts (e.g., Na salt, K salt, Li salt), ammonium salts, or salts of amines. However, the dichroic dyes are not limited to these and known dichroic dyes can be used. The azo compound, particularly in the form of a free acid, its salt, or its copper complex dye, has improved optical properties. This azo-based dye may be used alone or in combination with other azo compounds, and the combination is not limited. By using such azo compounds, in the transmittance at each wavelength obtained by measuring the transmittance of the polarizing element with the absorption axes of two substrates (A) parallel, the average transmittance at 520 nm to 590 nm is 30% or more, the absolute value of the difference between the average transmittance at 420 nm to 480 nm and the average transmittance at 520 nm to 590 nm is within 5%, and the absolute value of the difference between the average transmittance at 520 nm to 590 nm and the average transmittance at 590 nm to 660 nm is within 5%. Furthermore, in the transmittance at each wavelength obtained by measuring with the absorption axes of two substrates (A) perpendicular, the absolute value of the difference between the average transmittance at 420 nm to 480 nm and the average transmittance at 520 nm to 590 nm is within 2%, and the absolute value of the difference between the average transmittance at 520 nm to 590 nm and the average transmittance at 600 nm to 660 nm is within 2%. By adjusting to these values, a polarizing element for realizing the present invention is produced.

[0059] Hereinafter, as an element that can be impregnated with an azo compound, a method for producing a specific polarizing element will be described by taking a polyvinyl alcohol-based resin film as an example. The production method of the polyvinyl alcohol-based resin is not particularly limited and can be produced by a known method. As a production method, for example, it can be obtained by saponifying a polyvinyl acetate-based resin. Examples of the polyvinyl acetate-based resin include polyvinyl acetate which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The saponification degree of the polyvinyl alcohol-based resin is usually about 85 to 100 mol%, preferably 95 mol% or more. This polyvinyl alcohol-based resin may be further modified. For example, polyvinyl formal or polyvinyl acetal modified with aldehydes can also be used. The degree of polymerization of the polyvinyl alcohol-based resin means the viscosity average degree of polymerization and can be determined by a method well-known in the art. The viscosity average degree of polymerization is usually about 1000 to 10000, preferably about 1500 to 6000.

[0060] A film formed from such a polyvinyl alcohol-based resin is used as a raw film. The method for forming a film of the polyvinyl alcohol-based resin is not particularly limited and can be formed by a known method. In this case, the polyvinyl alcohol-based resin film may contain glycerin, ethylene glycol, propylene glycol, low molecular weight polyethylene glycol, etc. as a plasticizer. The amount of the plasticizer is 5 to 20% by weight, preferably 8 to 15% by weight. The film thickness of the raw film made of the polyvinyl alcohol-based resin is not particularly limited. For example, it is preferably about 5 μm to 150 μm, more preferably about 10 μm to 100 μm.

[0061] The obtained raw film is then subjected to a swelling process. The swelling treatment is applied by immersing it in a solution at 20°C to 50°C for 30 seconds to 10 minutes. Water is preferred as the solution. The draw ratio is preferably adjusted to 1.00 to 1.50 times, and more preferably 1.10 to 1.35 times. When shortening the time for producing the polarizing element, the swelling treatment may be omitted since it also swells during the dyeing treatment of the azo compound.

[0062] The swelling process is carried out by immersing the polyvinyl alcohol resin film in a solution at 20°C to 50°C for 30 seconds to 10 minutes. Water is preferred as the solution. When shortening the time for manufacturing the polarizing element, the swelling process can also be omitted since it also swells during the dyeing treatment of the dye.

[0063] After the swelling process, a dyeing process is carried out. In the dyeing process, impregnation can be performed using an azo compound (commonly known as a dichroic dye) shown in Non-Patent Document 1, etc. Since impregnating this azo compound is a process of coloring the color, it is referred to as a dyeing process. Here, as the azo compound, the dyes described in Non-Patent Document 1 and the azo compounds represented by Formula (1), etc. can adsorb and impregnate the dye into the polyvinyl alcohol film in the dyeing process. Or, after immersing in an aqueous solution impregnated with iodine and potassium iodide to adsorb iodine, each of the azo compounds represented by Formula (1) can be adsorbed and impregnated to obtain the base material (A) having the polarizing function of the present application. The azo compound adsorbed together with iodine may be other than the azo compound represented by Formula (1), and the azo compounds shown in Examples 1 to 5 of Patent Publication Sho 64-5623 or the azo compounds shown in Examples 1 to 4 of JP-A-03-12606 may also be used.

[0064]

Chemical formula

[0065] The dyeing process is not particularly limited as long as it is a method of adsorbing and impregnating a dye into a polyvinyl alcohol film. For example, the dyeing process is carried out by immersing a polyvinyl alcohol resin film in a solution containing a dichroic dye. The solution temperature in this process is preferably 5 to 60°C, more preferably 20 to 50°C, and particularly preferably 35 to 50°C. The time of immersion in the solution can be appropriately adjusted, but it is preferably adjusted within 30 seconds to 20 minutes, and more preferably 1 to 10 minutes. The dyeing method is preferably immersion in the solution, but it can also be carried out by applying the solution to the polyvinyl alcohol resin film.)

[0066] The solution containing the dichroic dye can contain, as a dyeing aid, sodium carbonate, sodium hydrogen carbonate, sodium chloride, sodium sulfate, anhydrous sodium sulfate, sodium tripolyphosphate, and the like. Their contents can be adjusted to any concentration depending on the dyeing property of the dye and the time and temperature, but the content of each is preferably 0 to 5% by weight, and more preferably 0.1 to 2% by weight. The azo compound which is a dichroic dye described in Non-Patent Document 1, the azo compound represented by the formula (1), etc. may be used as the free acid, or a salt of the compound may also be used. Such salts can also be used as alkali metal salts such as lithium salts, sodium salts, and potassium salts, or organic salts such as ammonium salts and alkylamine salts. Preferably, it is a sodium salt.)

[0067] After the dyeing process, a cleaning process (hereinafter referred to as cleaning process 1) can be performed before entering the next process. Cleaning process 1 is a process of cleaning the dye solvent adhering to the surface of the polyvinyl alcohol resin film in the dyeing process. By performing cleaning process 1, it is possible to suppress the transfer of the dye into the liquid to be processed next. In cleaning process 1, generally water is used as the cleaning solution. The cleaning method is preferably immersion in the solvent, but it can also be cleaned by applying the cleaning solution to the polyvinyl alcohol resin film. The cleaning time is not particularly limited, but is preferably 1 to 300 seconds, more preferably 1 to 60 seconds. The temperature of the cleaning solution in cleaning process 1 needs to be a temperature at which the hydrophilic polymer does not dissolve. Generally, the cleaning treatment is performed at 5 to 40°C. However, since there is no problem with the performance even without the process of cleaning process 1, this process can also be omitted.

[0068] After the dyeing process or cleaning process 1, a process of adding a crosslinking agent and / or a water resistance agent can be performed. As the crosslinking agent, for example, boron compounds such as boric acid, borax or ammonium borate, polyvalent aldehydes such as glyoxal or glutaraldehyde, polyvalent isocyanate-based compounds such as biuret type, isocyanurate type or blocked type, titanium-based compounds such as titanium oxysulfate, etc. can be used, but ethylene glycol glycidyl ether, polyamide epichlorohydrin, etc. can also be used. Examples of the water resistance agent include succinic peroxide, ammonium persulfate, calcium perchlorate, benzoin ethyl ether, ethylene glycol diglycidyl ether, glycerin diglycidyl ether, ammonium chloride or magnesium chloride, etc., but boric acid is preferably used. The process of adding a crosslinking agent and / or a water resistance agent is performed using at least one or more of the crosslinking agents and / or water resistance agents shown above. As the solvent at that time, water is preferred but not limited.

[0069] In the step of adding a crosslinking agent and / or a water resistance agent, the concentration of the crosslinking agent and / or the water resistance agent in the solvent, taking boric acid as an example, is preferably 0.1 to 6.0% by weight, more preferably 1.0 to 4.0% by weight based on the solvent. The temperature of the solvent in this step is preferably 5 to 70°C, more preferably 5 to 50°C. The method of adding the crosslinking agent and / or the water resistance agent to the polyvinyl alcohol resin film is preferably by immersion in the solvent, but the solution may also be applied or coated on the polyvinyl alcohol resin film. The treatment time in this step is preferably 30 seconds to 6 minutes, more preferably 1 to 5 minutes. However, if it is not essential to add the crosslinking agent and / or the water resistance agent and if the time needs to be shortened, or if the crosslinking treatment or the water resistance treatment is unnecessary, this treatment step may be omitted.

[0070] After performing the dyeing step, the first washing step, or the step of adding a crosslinking agent and / or a water resistance agent, a stretching step is carried out. The stretching step is a step of uniaxially stretching the polyvinyl alcohol film. The stretching method can be either a wet stretching method or a dry stretching method, and the present invention can be achieved by stretching at a stretching ratio of 3 times or more. The stretching ratio is preferably 3 times or more, preferably 5 to 7 times.

[0071] In the case of the dry stretching method, when the stretching heating medium is an air medium, the temperature of the air medium is preferably stretched at room temperature to 180°C. Also, the humidity is preferably treated in an atmosphere of 20 to 95% RH. Examples of the heating method include, but are not limited to, the inter-roll zone stretching method, the roll heating stretching method, the compression stretching method, the infrared heating stretching method, etc. The stretching step can be carried out in one stage, or it can also be carried out by multi-stage stretching of two or more stages.

[0072] In the case of the wet stretching method, stretching is carried out in water, a water-soluble organic solvent, or a mixed solution thereof. It is preferable to perform the stretching treatment while immersing in a solution containing a crosslinking agent and / or a water resistance agent. As the crosslinking agent, for example, boron compounds such as boric acid, borax or ammonium borate, polyvalent aldehydes such as glyoxal or glutaraldehyde, polyvalent isocyanate-based compounds such as biuret type, isocyanurate type or blocked type, titanium-based compounds such as titanium oxysulfate can be used, but ethylene glycol glycidyl ether, polyamide epichlorohydrin, etc. can also be used. Examples of the water resistance agent include succinic peroxide, ammonium persulfate, calcium perchlorate, benzoin ethyl ether, ethylene glycol diglycidyl ether, glycerin diglycidyl ether, ammonium chloride or magnesium chloride. Stretching is carried out in a solution containing at least one or more of the crosslinking agent and / or the water resistance agent shown above. Boric acid is preferable as the crosslinking agent.

[0073] The concentration of the crosslinking agent and / or the water resistance agent in the stretching step is preferably, for example, 0.5 to 15% by weight, more preferably 2.0 to 8.0% by weight. The stretching ratio is preferably 2 to 8 times, more preferably 5 to 7 times. The stretching temperature is preferably 40 to 60 °C, more preferably 45 to 58 °C. The stretching time is usually 30 seconds to 20 minutes, but more preferably 2 to 5 minutes. The wet stretching step can be carried out in one stage, but can also be carried out by multi-stage stretching of two or more stages.

[0074] In the case of the wet stretching method, stretching is carried out in water, a water-soluble organic solvent, or a mixed solution thereof. It is preferable to perform the stretching treatment while immersing in a solution containing a crosslinking agent and / or a water resistance agent. As the crosslinking agent, for example, boron compounds such as boric acid, borax, or ammonium borate, polyvalent aldehydes such as glyoxal or glutaraldehyde, polyvalent isocyanate compounds such as biuret type, isocyanurate type, or blocked type, titanium compounds such as titaniumoxysulfate, etc. can be used, but ethylene glycol glycidyl ether, polyamide epichlorohydrin, etc. can also be used. Examples of the water resistance agent include succinic peroxide, ammonium persulfate, calcium perchlorate, benzoin ethyl ether, ethylene glycol diglycidyl ether, glycerin diglycidyl ether, ammonium chloride, or magnesium chloride. Stretching is carried out in a solution containing at least one or more of the crosslinking agent and / or the water resistance agent shown above. Boric acid is preferable as the crosslinking agent.

[0075] The concentration of the crosslinking agent and / or the water resistance agent in the stretching step is preferably, for example, 0.5 to 15% by weight, more preferably 2.0 to 8.0% by weight. The stretching ratio is preferably 2 to 8 times, more preferably 5 to 7 times. The stretching temperature is preferably treated at 40 to 60°C, more preferably 45 to 58°C. The stretching time is usually 30 seconds to 20 minutes, but more preferably 2 to 5 minutes. The wet stretching step can be carried out in one stage, but can also be carried out by multi-stage stretching of two or more stages.

[0076] After the stretching step, since precipitation of the crosslinking agent and / or the water resistance agent or foreign substances may adhere to the film surface, a cleaning step (hereinafter referred to as cleaning step 2) for cleaning the film surface can be carried out. The cleaning time is preferably 1 second to 5 minutes. The cleaning method is preferably immersion in a cleaning solution, but the solution can also be cleaned by coating or applying it to the polyvinyl alcohol resin film. The cleaning treatment can be carried out in one stage, or multi-stage treatment of two or more stages can be carried out. The solution temperature of the cleaning step is not particularly limited, but is usually 5 to 50°C, preferably 10 to 40°C.

[0077] Examples of the solvent used in the treatment steps up to this point include, but are not limited to, solvents such as water, dimethyl sulfoxide, N-methylpyrrolidone, methanol, ethanol, propanol, isopropyl alcohol, glycerin, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, or trimethylolpropane, and amines such as ethylenediamine or diethylenetriamine. A mixture of one or more of these solvents can also be used. The most preferred solvent is water.

[0078] After the stretching step or the second washing step, a drying step of the film is performed. The drying treatment can be carried out by natural drying, but in order to enhance the drying efficiency, surface moisture removal can be performed by compression with a roll, an air knife, or a water-absorbing roll, and / or blow drying can also be performed. As the drying treatment temperature, it is preferably dried at 20 to 100 °C, and more preferably at 60 to 100 °C. The drying treatment time can be applied from 30 seconds to 20 minutes, but is preferably 5 to 10 minutes.

[0079] By the above method, a polarizing element of the substrate (A) having a polarizing function, that is, containing an azo compound, in which the average transmittance at 520 nm to 590 nm is 30% or more in the transmittance obtained by measuring with the absorption axes of two substrates (A) parallel, and the absolute value of the difference between the average transmittance at 420 nm to 480 nm and the average transmittance at 520 nm to 590 nm is within 5%, and the absolute value of the difference between the average transmittance at 520 nm to 590 nm and the average transmittance at 590 nm to 660 nm is within 5%, and further, in the transmittance at each wavelength obtained by measuring with the absorption axes of two substrates (A) orthogonal, the absolute value of the difference between the average transmittance at 420 nm to 480 nm and the average transmittance at 520 nm to 590 nm is within 2%, and the absolute value of the difference between the average transmittance at 520 nm to 590 nm and the average transmittance at 600 nm to 660 nm is within 2% can be obtained.

[0080] The obtained polarizing element is made into a polarizing plate by providing a transparent protective layer on one or both of its surfaces. The transparent protective layer can be provided as a coating layer made of a polymer or as a laminated layer of a film. As the transparent polymer or film forming the transparent protective layer, a transparent polymer or film having high mechanical strength and good thermal stability is preferred. Examples of substances used as the transparent protective layer include cellulose acetate resins such as triacetyl cellulose and diacetyl cellulose or their films, acrylic resins or their films, polyvinyl chloride resins or their films, nylon resins or their films, polyester resins or their films, polyarylate resins or their films, cyclic polyolefin resins having cyclic olefins such as norbornene as monomers or their films, polyethylene, polypropylene, polyolefins having a cyclic or norbornene skeleton or their copolymers, resins or polymers having imide and / or amide in the main chain or side chain or their films, etc. Also, a resin or its film having liquid crystallinity can be provided as the transparent protective layer. The thickness of the protective film is, for example, about 0.5 to 200 μm. The polarizing plate is produced by providing one or more layers of the same or different resins or films on one or both sides.

[0081] In some cases, when the obtained polarizing plate is bonded to a display device such as a liquid crystal or organic electroluminescence (commonly known as OLED or OEL), various functional layers for improving the viewing angle and / or contrast, a layer having luminance improvement properties, or a film can be provided on the surface of the protective layer or film that will later become the non-exposed surface. It is preferable to use an adhesive to bond the polarizing plate to these films or display devices.

[0082] In addition, the various functional layers refer to layers or films that control the phase difference. In particular, in order to impart antireflection properties, a retardation plate adjusted to a quarter-wave retardation with respect to 550 nm with high visual sensitivity (hereinafter referred to as 1 / 4λ) is generally bonded to a polarizing element or a polarizing plate at 45° with respect to the absorption axis of the polarizing element or the polarizing plate. The quarter-wave retardation value is a retardation plate adjusted to 120 nm to 160 nm, preferably 130 nm to 145 nm.

[0083] However, since the antireflection function may be insufficient with only 1 / 4λ, in order to further improve the antireflection function, there is also a method of improving antireflection by using two retardation plates bonded at 15° with respect to the absorption axis of the polarizing plate and 75° for 1 / 4λ, where the retardation plate is adjusted to a retardation value of 240 nm to 300 nm (hereinafter abbreviated as 1 / 2λ).

[0084] Furthermore, this polarizing plate may have various known functional layers such as an antireflection layer, an antiglare layer, and a hard coat layer on the other surface, that is, the exposed surface of the protective layer or film. Although a coating method is preferable for producing the layer having various functions, a film having the function can also be bonded via an adhesive or a pressure-sensitive adhesive.

[0085] By the above method, in the wavelength transmittance obtained by measuring with the absorption axes of two substrates (A) parallel, the average transmittance at 520 nm to 590 nm is 30% or more, the absolute value of the difference between the average transmittance at 420 nm to 480 nm and the average transmittance at 520 nm to 590 nm is within 5%, and the absolute value of the difference between the average transmittance at 520 nm to 590 nm and the average transmittance at 590 nm to 660 nm is within 5%. Furthermore, in the wavelength transmittance obtained by measuring with the absorption axes of two substrates (A) orthogonal, the absolute value of the difference between the average transmittance at 420 nm to 480 nm and the average transmittance at 520 nm to 590 nm is within 2%, and the absolute value of the difference between the average transmittance at 520 nm to 590 nm and the average transmittance at 600 nm to 660 nm is within 2%, a polarizing element and a polarizing plate can be obtained. The liquid crystal display device using the polarizing element or polarizing plate of the present invention can be bright and have high luminance. As a result, a liquid crystal display device with high reliability, high contrast over a long period, and high color reproducibility is obtained.

[0086] The polarizing plate of the present invention thus obtained is used as a base material (A) having a polarizing function by providing a protective layer, a functional layer, a support such as plate glass, etc. as needed, and is used in liquid crystal projectors, calculators, watches, notebook computers, word processors, liquid crystal TVs, polarizing lenses, polarized glasses, car navigation systems, and indoor and outdoor measuring instruments and displays, etc. In particular, it is suitable for reflective liquid crystal display devices, transflective liquid crystal display devices, organic electroluminescence, etc.

[0087] A general reflective liquid crystal display device has a configuration of a reflector, a polarizing plate, a liquid crystal cell, and a polarizing plate in order from the back side. In order to improve its display quality, it is a general configuration to use a light diffusing plate or a retardation plate (for example, 1 / 4λ).

[0088] With respect to such a general configuration, by using the base material (A) having a polarizing function of the present application, a configuration of a diffusive reflector, a base material (A) having a polarizing function, a liquid crystal cell, and a base material (A) having a polarizing function in order from the back side, or a configuration exemplified by a reflector, a diffusing plate, a base material (A) having a polarizing function, a liquid crystal cell, and a base material (A) having a polarizing function in order from the back side, it becomes possible to provide a display device that can display white like high-quality paper during white display and pitch-black black during black display, so the display quality is dramatically improved.

[0089] Although it is common to provide a light diffusing plate between a reflector and a polarizing plate on the back side, as long as its light diffusing effect can be obtained, its laminated structure is not limited. Alternatively, as shown in Non-Patent Document 3, methods such as a single polarizing plate method (SPD mode) and configurations such as those shown in Non-Patent Document 4 have been reported. In such configurations, in a general polarizing plate, when attempting to display a pitch-black color, it becomes a white display with a yellow color presentation in white display, and conversely, when attempting to display a white color like high-quality paper, it shows a blue color presentation when displaying black.

[0090] Due to such problems, in reflective liquid crystals, particularly in color reflective liquid crystal display devices, until now, it has been necessary to improve the white color during white display and the black color during black display using color filters or liquid crystal elements. As a result, the reflectivity has been considered low, the display has been considered dark, and the display quality has been considered low. By using a substrate (A) having a polarizing function in such a reflective liquid crystal display device, the hue generated by the yellow color presentation during white display and the blue color presentation during black display that a polarizing plate has is improved. Since there is no transmittance dependency for each wavelength whether in the parallel position or the orthogonal position, a display device can be provided that displays a white color like high-quality paper during white display and a pitch-black color during black display.

[0091] In particular, since the transmittance is constant and there is no wavelength dependency of the transmittance at each wavelength, it is particularly effective for black-and-white reflective displays that cannot correct colors with a color filter. In addition, for the substrate (A) having this polarizing function, as the required transmittance range, it is possible to adjust the transmittance arbitrarily at 25% to 45% as the average transmittance of each wavelength from 520 nm to 590 nm measured with the absorption axes of two substrates parallel. Therefore, it is possible to achieve improving the luminance during display and also improving the contrast.

[0092] Furthermore, in order to improve the display quality, a substrate (A) having a polarization function is laminated with a reflective polarizing plate with a liquid crystal cell interposed therebetween, and a substrate having a light diffusion function is provided. By installing the substrate (A) having a polarization function on the observer side with respect to the liquid crystal cell, the display quality is improved. As the reflective polarizing plate, a polarizer provided with regular unevenness as exemplified in Patent No. 4162645 and Patent No. 4442760, an alternating lamination type of thermoplastic resin such as those disclosed in JP-A-2006-215175 and JP-A-2007-298634, a BEF series manufactured by 3M, particularly the DBEF series, or a resin molding type having a special shape such as BEFRP can be used.

[0093] Also, an anisotropic light diffusion plate as described in JP-A-2012-37611 can be used as a reflective polarizing plate because it has a polarization function due to anisotropic light diffusion. In an exemplary configuration of a reflective plate, a liquid crystal cell, a retardation plate (e.g., 1 / 4λ), and a substrate (A) having a polarization function in this order from the back side, it is preferable to provide the anisotropic light diffusion plate between the reflective plate and the liquid crystal cell, between the liquid crystal cell and the retardation plate, or between the retardation plate and the polarizing plate.

[0094] Furthermore, it is also applicable to an active matrix type reflective display. This can be achieved by a reflective liquid crystal display device in which a substrate having a light diffusion function is provided between a substrate (A) having a polarization function and a liquid crystal cell, and the electrodes of the liquid crystal cell are mirror reflection type electrodes. As a specific configuration example, it is a configuration of a mirror reflection type electrode, a liquid crystal cell, a light diffusion plate, and a substrate (A) having a polarization function in this order from the back side. At that time, a retardation plate may be provided between any of the layers to improve visibility.

[0095] In particular, since active matrix type reflective displays are suitably used for reflective color liquid crystal display devices, they are easily affected by the color of the polarizing element or polarizing plate. They have almost constant transmittance without wavelength dependence in the transmittance of each wavelength in the parallel and orthogonal positions, no color shift, and a substrate with a high degree of polarization is required. For such reflective color liquid crystal displays, the substrate (A) having a polarizing function is effective, and the display device provided therewith becomes a display device having very high color rendering properties.

[0096] Also, as an application to an active matrix type reflective display, as described in Non-Patent Document 4, the electrodes of the liquid crystal cell are made uneven by a resin or the like, and a diffusion reflective electrode that reflects using an aluminum electrode without using a transparent ITO electrode can improve the display quality more. As a specific configuration example, it is a configuration of a diffusion type reflective electrode, a liquid crystal cell, and a substrate (A) having a polarizing function in order from the back side. At that time, in order to improve visibility, a retardation plate may be provided between any layers. Also, a substrate having a light diffusion function may be provided between any layers, and further light diffusibility may be provided to improve visibility.

[0097] By the above method, even in a reflective liquid crystal device that has been regarded as having low display quality, the display quality can be dramatically improved, the color of the display device caused by the yellow coloration during white display and the blue coloration during black display of the polarizing plate can be improved, white is displayed during white display, black is displayed during black display, and a display device having high color rendering properties in a reflective color liquid crystal display device can be provided.

[0098] Furthermore, as for the transmittance range of the substrate (A) having a polarizing function, since it is possible to adjust an arbitrary transmittance at 25% to 45% as the average transmittance of each wavelength from 520 nm to 590 nm measured with the absorption axes of two substrates (A) parallel, it is possible to achieve an improvement in the brightness during display and an improvement in the contrast. Also, depending on the configuration of the reflective liquid crystal, the display quality can be improved in each stage.

Example

[0099] Example 1 A display device according to a first embodiment of the present invention will be described with reference to FIG. 2. FIG. 2(a) is a vertical cross-sectional view of the display device according to the first embodiment, in which a base material (A) 1, a retardation plate 2, a diffusion plate 3, a first glass substrate 4, a color filter 5, a counter electrode (ITO 6), a liquid crystal layer 7, a reflector / pixel electrode (Al) 8, and a second glass substrate 9 are arranged in this order from the top surface (observer side) (hereinafter simply referred to as the top surface) of the display device. The aspect ratio of the drawing is different from the actual ratio for ease of understanding. In the following embodiments, parts with the same reference numerals represent the same objects. FIG. 2(b) is a plan view of the color filter 5, showing that it is made up of red 5a, green 5b, and blue 5c pixel elements. In an actual display device, the period of this red, green, and blue pattern is repeated as many times as the number of pixels.

[0100] The substrate (A) 1 is a dye-based polarizing plate obtained by dyeing PVA with a dye. FIG. 3 is a diagram showing the relationship between the parallel transmittance and the crossed transmittance of a polarizing plate made of the same material as the substrate (A) 1. That is, a dye-based polarizing plate is made by adjusting the dye concentration using the same material as the substrate (A) 1 used, and the relationship between the transmittance (parallel transmittance) obtained by measuring the absorption axes of two polarizing plates parallel to each other and the transmittance (crossed transmittance) obtained by measuring the absorption axes of two polarizing plates perpendicular to each other is shown. From FIG. 3, it can be seen that the crossed transmittance also increases as the parallel transmittance increases. FIG. 4 is a diagram showing the relationship between the parallel transmittance and the contrast. From FIG. 4, it can be seen that the contrast decreases as the parallel transmittance increases. Here, the contrast is the contrast of the polarizing plate expressed by the following formula. Contrast = Parallel transmittance / Cross transmittance

[0101] The contrast of the polarizing plate needs to be 10 or more, and the parallel transmittance of the base material (A)1 was adjusted to a value of 36% to 39% in order to suppress the decrease in reflectance. In a reflective liquid crystal display device, it is important to increase the reflectance to achieve a bright display. In this example, the NTSC ratio of the color filter was adjusted to 5% to 15% so that a reflectance of 20% or more could be obtained and a good color display could be realized.

[0102] By the way, in terms of reflectance, the product of the transmittance of the color filter and the parallel transmittance of the base material (A)1 is the most important factor. For example, referring to FIG. 1 showing the relationship between the NTSC ratio and the transmittance when light passes through the color filter twice, the transmittance of the color filter when the NTSC ratio of the color filter is 5% to 15% is 70 to 90%, a reflectance of 20% or more can be obtained, and a good color display can be realized. Note that the color filter can adjust the color density by changing the layer thickness and the pigment concentration.

[0103] Also, in the transmittance obtained by measuring with the absorption axes of the two base materials (A) parallel, the absolute value of the difference between the average transmittance of 420 nm to 480 nm and the average transmittance of 520 nm to 590 nm is 1.0% to 2%, and the absolute value of the difference between the average transmittance of 520 nm to 590 nm and the average transmittance of 590 nm to 660 nm is 1.0% to 2.0%, Furthermore, in the transmittance at each wavelength obtained by measuring with the absorption axes of the two base materials orthogonal to each other, the absolute value of the difference between the average transmittance of 420 nm to 480 nm and the average transmittance of 520 nm to 590 nm is 0.5% to 1.0%, the absolute value of the difference between the average transmittance of 520 nm to 590 nm and the average transmittance of 600 nm to 660 nm was adjusted to be 0.5% to 1%. In the reflective liquid crystal display device of Example 1 manufactured in such a manner, a highly reflective, bright, high-quality white display and black display without coloring, and an excellent color display were realized.

[0104] (Example 2) A display device according to a second embodiment of the present invention will be described with reference to Fig. 5. Fig. 5(a) is a vertical cross-sectional view of the display device according to the second embodiment, in which, from the top, a base material (A) 1, a retardation plate 2, a diffusion plate 3, a glass substrate 4, a color filter 51 with a transparent region, a counter electrode (ITO) 6, a liquid crystal layer 7, a reflector / pixel electrode (Al) 8, and a second glass substrate 9 are arranged. The aspect ratio of the drawing is different from the actual ratio in order to make the effect easier to understand.

[0105] FIG. 5(b) is a plan view of the color filter 51 having a transparent region, and shows that the color filter 51 is made up of red 51a, green 51b, and blue 51c pixel elements. A transparent region without a color layer is provided in a part of each color region of the color filter 51. By changing the area of ​​the transparent region, the NTSC ratio of the color filter 51 can be adjusted to a range of 1% to 20%, and the reflectance can be increased. It is more preferable to provide the transparent region in the center, since this reduces variations during production. Furthermore, by using the base material (A) 1, coloring of the transparent region formed in the color filter 51 can be prevented, and high-quality white and black display and excellent color display without coloring can be realized while having a high reflectance.

[0106] Example 3 The pixel configuration of the third embodiment of the present invention is different from that of the second embodiment, and is made up of red, green, blue, and transparent pixels. In addition to the color filter 52 and the color layers of red 52a, green 52b, and blue 52c, a transparent pixel 52d without a color layer is formed. By adding the transparent pixel 52d to the color layers 52a to 52c, the NTSC ratio is reduced to a range of 1% to 20%, the reflectance is improved, and a bright display is possible.

[0107] In addition, by making each of the color layers 52a to 52c and the transparent pixels 52d substantially square and arranging them in a cross shape, the invalid area becomes smaller than when arranging them side by side, and the aperture ratio can be increased, enabling a color display with a high reflectance to be realized. Further, by using the base material (A) 1, coloring of the transparent pixels 52d formed in the color filter 52 is also prevented, and high-quality white display, black display, and excellent color display without coloring can be realized while having a high reflectance.

[0108] (Example 4) Example 4 of the present invention is shown in FIG. 7. Compared with Examples 2 and 3, the pixel configuration is different, and it is composed of translucent pixels of red, green close to red, blue, and green close to blue. The color filter 53 is composed of color layers of red 53a, green close to red 53b, blue 53c, and green close to blue 53d. In the red 53a, green close to red 53b, blue 53c, and green close to blue 53d of the color filter 53, transparent regions without color layers are provided in part of each color layer. By changing the area of the transparent region, the NTSC ratio of the color filter 53 can be adjusted to the range of 1% to 20% without changing the material or thickness of the color filter 53, and the reflectance can be increased.

[0109] In addition, by making each of the four pixels substantially square and arranging them in a cross shape, the invalid area becomes smaller than when arranging them side by side, and the aperture ratio can be increased, enabling a color display with a high reflectance to be realized. Further, by using the base material (A) 1, coloring of the transparent regions formed in the color filter 53 is also prevented, and high-quality white display, black display, and excellent color display without coloring can be realized while having a high reflectance.

[0110] (Example 5) Example 5 of the present invention is shown in FIG. 8. In Example 5, a reflector and display electrode (Al) having a diffusion shape 81 is formed. Due to the diffusion function of the reflector and the effect of the diffusion plate 3, external light can be diffused over a wider range.

[0111] (Example 6) Example 6 of the present invention is shown in Fig. 9. In Example 6, a reflector 10 is disposed on the rear side of the display device, and a second base material 11 and a second glass substrate 9 are disposed in this order on the reflector 10. A transparent pixel electrode (ITO or IZO) 82 is disposed on the second glass substrate 9. With this structure, it is not necessary to form a reflector in the region sandwiched between the first glass substrate 4 and the second glass substrate 9, and by using a reflective polarizing plate that reflects a specific polarized light as the reflector 10, it is also possible to display using light that enters from the rear side via the reflective polarizing plate. [Explanation of symbols]

[0112] 1 Base material (A), 2 Retardation plate, 3 Diffusion plate, 4 First glass substrate, 5 Color filter, 6 Counter electrode (ITO), 7 Liquid crystal layer, 8 Reflector / pixel electrode (Al), 9 Second glass substrate, 5a Red region of color filter, 5b Green region of color filter, 5c Blue region of color filter, 51 Color filter with transparent region, 51a Red region of color filter with transparent region, 51b Green region of color filter with transparent region, 51c Blue region of color filter with transparent region, 51d Red region of color filter with transparent region, 52a Red region of color filter of Example 3, 52b Green region of color filter of Example 3, 52c Blue region of color filter of Example 3, 52d Transparent region of color filter of Example 3, 53a Red region of color filter of Example 4, 53b Red-leaning green region of color filter of Example 4, 53c Blue region of the color filter of Example 4, 53d blue-leaning green region of the color filter of Example 4, 81 reflector / display electrode (Al) having a diffused shape, 82 transparent pixel electrode (ITO or IZO)

Claims

1. containing an azo compound represented by formula (1) or a salt thereof, 【Chemical 1】 (wherein A １ represents a phenyl group or a naphthyl group having a substituent, and R １ or R ２ each independently represents a hydrogen atom, a lower alkyl group, a lower alkoxy group, a sulfo group, or a lower alkoxy group having a sulfo group, and X １ represents a phenylamino group which may have a substituent.) in the transmittance obtained by measuring with the absorption axes of two substrates parallel, the average transmittance at 520 nm to 590 nm is 30% or more, the absolute value of the difference between the average transmittance at 420 nm to 480 nm and the average transmittance at 520 nm to 590 nm is within 5%, and the absolute value of the difference between the average transmittance at 520 nm to 590 nm and the average transmittance at 590 nm to 660 nm is within 5%, and further, in the transmittance at each wavelength obtained by measuring with the absorption axes of the two substrates orthogonal, the absolute value of the difference between the average transmittance at 420 nm to 480 nm and the average transmittance at 520 nm to 590 nm is within 2%, and the absolute value of the difference between the average transmittance at 520 nm to 590 nm and the average transmittance at 600 nm to 660 nm is within 2%, a substrate having a polarizing function, a color filter, comprising a display device characterized in that the NTSC ratio when light passes through the color filter twice is 1% or more and 5% or less.

2. The color filter has a colorless and transparent region, and the area of the colorless and transparent region is 1 / 4 or more of the total area of the color filter. The display device according to claim 1.

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